A patient with a mental illness suffered extensive burns when he set fire to himself at Airedale General Hospital, Steeton, today.
The man - in his 60s - walked out of a lavatory with his night clothes on fire at 5.13 am.
A member of staff managed to put out the flames with a fire extinguisher.
He was transferred for specialist treatment at the burns unit at Pinderfields Hospital, Wakefield.
Hospital bosses immediately started an internal inquiry into the incident.
Airedale NHS Trust chief executive, Bob Allen, said the man's identity was not being released, but he confirmed he had been a patient on the acute mental illness ward for several months.
"This is a tragedy for him and his family," said Mr Allen.
The man, a patient on ward four, went to the bathroom, locked himself in and came out alight, said Mr Allen.
"He had managed to get lighter fuel and a lighter from somewhere and set fire to himself. He came out of the lavatory burning and an extinguisher was used to put out the flames but not before he suffered burns.
"He had been under close observation every 15 minutes but when somebody goes to the lavatory nobody goes in with them," said Mr Allen.
The man's burns were to an extent they could not be treated at Airedale and he had to be transferred immediately to Wakefield but his injuries were not thought to be life-threatening, said Mr Allen.
The incident comes only weeks after two women metal health ward patients - one in a wheelchair - were killed when they were hit by a train.
They had left the ward unseen and managed to get on to the nearby Leeds to Skipton line. The health trust is about to start an inquiry into their deaths.
Health watchdog, Airedale Community Health Council, has questioned the capacity of the hospital to nurse patients who have serious mental illness and threaten suicide.
Its chief officer John Godward said today: "We have questioned whether the wards are in the correct location because they are near to the railway line and the River Aire.
"And we have questioned whether the levels of staff are able to cope with the serious cases they get."
He said there had been a similar incident last year involving a woman mental health patient tried to set fire to herself and inhale the smoke.
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